Military helicopters took off on Monday with four Spanish rescuers to search for a missing pair of European climbers on Nanga Parbat, the world's ninth highest mountain.

Italian Daniele Nardi and Briton Tom Ballard, whose mother died on K2 in 1995, have been missing for a week on the summit known as “Killer Mountain.”

Bad weather had foiled search plans on Sunday but as the skies cleared on Monday, two military helicopters took off from the northern town of Skardu with four Spanish rescuers onboard.

Karrar Haidri, secretary of the Alpine Club of Pakistan, said Spaniard Alex Txikon and his three colleagues, including a physician, would try and help find the missing climbers.

They will join Pakistani mountaineer Ali Sadpara who is already at base camp waiting for the search to begin, Haidri said, adding that he hopes the improved weather would allow the team to undertake the search during the day.

Rescuers also plan to use a drone in their search efforts, Haidri said.

Italian Ambassador Stefano Pontecorvo, who has been following the search, tweeted on Monday that the army helicopters took off from Skardu to drop Txikon and the rescue team at Camp-1 on Nanga Parbat.

Despite being dubbed “Killer Mountain” because of its dangerous conditions, the summit of Nanga Parbat has long drawn thrill-seeking climbers. Located in Pakistan's Gilgit Baltistan area, it is the ninth highest mountain in the world with height of 8,126 meters (26,660 feet).

Nardi and Ballard set out on the climb on Feb 22, making it to the fourth base camp by the following day.

The pair last made contact on Feb 24 from around an elevation of some 6,300 meters (nearly 20,700 feet) on Nanga Parbat.

Pakistan dispatched search helicopters last week despite the closure of its airspace amid tensions with neighbouring India over the disputed Himalayan region of Kashmir but didn't manage to find the climbers.

Sadpara, who joined the search team, saw a snow-covered tent of the climbers on Thursday. Nardi's team had said in a Facebook post that traces of an avalanche were evident in the area.

Nardi, 42, from near Rome, has attempted the Nanga Parbat summit in winter several times in the past. Ballard, 30, is the son of British climber Alison Hargreaves, the first woman to scale Mount Everest alone. She died at age 33 while descending the summit of K2.

Ballard in 2015 became the first person ever to solo climb all six major north faces of the Alps in one winter.